The term "spatial light modulator" as used herein is defined to include not only devices which modulate light from an external light source but also devices which emit light of a modulatable intensity.
EP 0 625 861 discloses an SLM having a picture element (pixel) pattern which is suitable for generating contiguous viewing windows when used in an autostereoscopic display. For instance, when used with a parallax device such as a parallax barrier or lenticular screen, there is a smooth transition from one view to another when an observer moves laterally with respect to the display. In particular, undesirable black band features and image intensity modulation are reduced or eliminated. Such a display is suitable for tracking the movement of an observer electronically so as to increase the observer viewing freedom while perceiving the 3D effect. Suitable lateral and longitudinal tracking techniques are disclosed in EP 0 726 482 and EP 0 721 131. Further, a technique for manufacturing an SLM of this type is disclosed in GB 2 302 978 and EP 0 752 609. GB 2 309 609 and EP 0 786 912 discloses an SLM having a different pixel pattern. In this case, adjacent pixels overlap horizontally so that, when used in an autostereoscopic 3D display, the viewing windows overlap laterally. This type of display is also suitable for providing electronic tracking of an observer.
EP 0 404 289 discloses an autostereoscopic 3D display comprising a flat display panel associated with a lenticular screen employing pitch changes and thickness changes. Tracking of the position of an observer so that viewing windows follow the observer is achieved by moving the lenticular screen laterally and longitudinally with respect to the display panel.
EP 0 354 851 discloses an autostereoscopic 3D display in which an image source is located behind a lenticular screen. In order to provide observer tracking, the image information supplied to the image source pixels is changed in accordance with the observer position so as to keep the observer in the correct stereoscopic zone while permitting movement.
J. B. Eichenlaub, "An autostereoscopic Display with High Brightness and Power Efficiency", SPIE Vol. 2177, 4-15 (1994) discloses a rear illumination of the autostereoscopic display in which a set of optics produces a set of thin vertical light lines behind an SLM. These light lines co-operate with the pixel apertures of the SLM to provide directional illumination. Observer tracking is achieved by moving the positions of the light lines relative to the SLM. The light lines are produced by imaging a light source through a lenticular screen to provide vertical thin bright images on a diffuser, which images act as thin strip sources of non-directional light. Several light sources are provided and, by switching between the different light sources, the images on the diffuser change position so as to simulate a moving light source.
C. Van Berkel, D. W. Parker, A. R. Franklin, "Multi-View 3D-LCD", IS&T/SPIE Symposium on Electronic Imaging: Stereoscopic Displays and Applications VIII, (San Jose, USA, 1996) disclose an autostereoscopic display comprising a liquid crystal device (LCD) disposed behind a lenticular screen. The LCD is of a standard type but has a relatively high aperture ratio (ratio of total pixel area to panel area).
The autostereoscopic 3D display illustrated diagrammatically in FIG. 1 of the accompanying drawings comprises a known type of SLM 1 associated with a parallax device in the form of a lenticular screen 2. The SLM 1 has pixels arranged as horizontal rows and vertical columns. The display is of the type which provides three views in three adjacent viewing regions or windows for an observer. Thus, three columns of pixels are disposed behind each lenticule, such as 3, of the screen 2. The columns behind the lenticule 3 are indicated in FIG. 1 as providing views 1, 2 and 3. The lenticule images the pixel columns into the three adjacent viewing windows.
The pixel columns display vertical slices of three two dimensional (2D) views taken in directions corresponding to the directions in which the three views are visible to an observer observing the 3D display. Thus, when the eyes of an observer are located in adjacent viewing windows, the observer sees a 3D image autostereoscopically i.e. without requiring any viewing aids.
The pixels such as 4 have the shape of two adjacent rectangles as defined by a black mask 5 of the SLM 1. Further, the pixel columns are separated from each other by vertical black mask strips. This gives rise to variations in illumination intensity illustrated in FIG. 2 of the accompanying drawings which is a diagrammatic plan view showing the SLM 1 and the lenticular screen 2. Each lenticule images the three associated columns of pixels 4 into viewing directions of varying illumination. For instance, the column containing the pixel 4 shown in FIG. 1 gives rise to a region 6 of maximum illumination corresponding to the portion of the pixel of greatest height, a region 7 of reduced illumination corresponding to the portion of the pixel of reduced vertical height, and a dark region 8 in which the vertical black mask strip between adjacent columns of pixels is imaged by the lenticule 3. Thus, as an observer moves with respect to the display, the image intensity varies substantially and gives rise to undesirable visual artefacts. Longitudinal and lateral viewing freedom is thus adversely Affected.
Irregular illumination as illustrated in FIG. 2 is caused by differing vertical extents within the pixel shape. When light transmitted through the pixels is imaged through the cylindrical lenses formed by the lenticules of the lenticular screen, there is no restriction on the vertical spreading of light. Thus, at a viewing window plane, a vertical strip of illumination is produced by each part of the pixel. The intensity of the illumination is directly proportional to the vertical extent of the pixel. Thus, for constant illumination, a rectangular pixel shape is desirable. Also, in order to avoid dark regions between illuminated regions, the columns of pixels should be horizontally contiguous, at least below each lenticule.
FIG. 3 of the accompanying drawings illustrates an SLM of the type disclosed in EP 0 625 861. The pixels are arranged as rows and columns such that the pixels in each column are horizontally contiguous with the pixels of the or each adjacent column. Further, the pixels are of rectangular shape so as to have constant vertical extent across the width of the pixel. As shown in FIG. 4 of the accompanying drawings, a display using this pixel arrangement provides contiguous viewing regions 9, 10 and 11 whose illumination intensity is substantially constant and unaffected by lateral movement of an observer.
In order to interleave the pixels of adjacent rows of the layout shown in FIG. 3, the gaps between pixels must be at least as large as the pixels themselves. Thus, the maximum theoretical aperture ratio of an SLM 1 of the type shown in FIG. 3 is 50%. However, in practice, space must be left between the pixels for the routing of electrical connections so that the maximum aperture ratio in practice is less than 50%.
Space must be allowed between the pixel apertures for the routing of conductors controlling the pixels. Such conductors generally comprise row conductors (normally referred to as "gate lines" in standard thin film transistor LCDs), which extend essentially horizontally and connect all the pixels in each row, and column conductors (referred to as "source lines") which extend essentially vertically and interconnect the pixels in each column. In matrix addressed devices, the gate and source lines are addressed in sequence to control the pixels so as to avoid having an individual electrode connection for each pixel.